xen/xenpaging.machine_to_phys_mapping.patch

Subject: xenpaging: update machine_to_phys_mapping during page-in and page-out

The machine_to_phys_mapping array needs updating during page-out.
If a page is gone, a call to get_gpfn_from_mfn will still return the old
gfn for an already paged-out page.  This happens when the entire guest
ram is paged-out before xen_vga_populate_vram() runs.  Then
XENMEM_populate_physmap is called with gfn 0xff000.  A new page is
allocated with alloc_domheap_pages.  This new page does not have a gfn
yet.  However, in guest_physmap_add_entry() the passed mfn maps still to
an old gfn.  This old gfn is paged-out and has no mfn anymore.  As a
result, the ASSERT() triggers because p2m_is_ram() is true for
p2m_ram_paging* types.

If the machine_to_phys_mapping array is updated properly, both loops in
guest_physmap_add_entry() turn into no-ops for the new page and the
mfn/gfn mapping will be done at the end of the function.


The same thing needs to happen dring a page-in.
If XENMEM_add_to_physmap is used with XENMAPSPACE_gmfn,
get_gpfn_from_mfn() will return an appearently valid gfn.  As a result,
guest_physmap_remove_page() is called.  The ASSERT in p2m_remove_page
triggers because the passed mfn does not match the old mfn for the
passed gfn.

Signed-off-by: Olaf Hering <olaf@aepfle.de>

---
v2:
  call set_gpfn_from_mfn only if mfn is valid
 xen/arch/x86/mm/p2m.c |   14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

--- xen-4.0.1-testing.orig/xen/arch/x86/mm/p2m.c
+++ xen-4.0.1-testing/xen/arch/x86/mm/p2m.c
@@ -2524,6 +2524,7 @@ int p2m_mem_paging_evict(struct domain *
     /* Remove mapping from p2m table */
     p2m_lock(d->arch.p2m);
     set_p2m_entry(d, gfn, _mfn(PAGING_MFN), 0, p2m_ram_paged);
+    set_gpfn_from_mfn(mfn_x(mfn), INVALID_M2P_ENTRY);
     p2m_unlock(d->arch.p2m);
 
     /* Put the page back so it gets freed */
@@ -2598,9 +2599,16 @@ void p2m_mem_paging_resume(struct domain
 
     /* Fix p2m entry */
     mfn = gfn_to_mfn(d, rsp.gfn, &p2mt);
-    p2m_lock(d->arch.p2m);
-    set_p2m_entry(d, rsp.gfn, mfn, 0, p2m_ram_rw);
-    p2m_unlock(d->arch.p2m);
+    if (mfn_valid(mfn))
+    {
+        p2m_lock(d->arch.p2m);
+        set_p2m_entry(d, rsp.gfn, mfn, 0, p2m_ram_rw);
+        set_gpfn_from_mfn(mfn_x(mfn), rsp.gfn);
+        p2m_unlock(d->arch.p2m);
+    } else {
+        gdprintk(XENLOG_ERR, "invalid mfn %lx for gfn %lx p2mt %x flags %lx\n",
+            mfn_x(mfn), rsp.gfn, p2mt, (unsigned long)rsp.flags);
+    }
 
     /* Unpause domain */
     if ( rsp.flags & MEM_EVENT_FLAG_VCPU_PAUSED )